DE10022722C5 - Safety switching device for safe switching on and off of an electrical consumer - Google Patents

Abstract

Safety switching device for safe switching on and off of an electrical load (24), in particular an electric drive, with an electromechanical switching element (12) having at least one adjustable working contact (14), with a power supply (26) for generating an operating voltage (U '_B; U _B ) for the switching element (12), and with a lowering unit (30), the operating voltage supplied to the switching element (12) (U '_B; U _B ) in response to an operating state of the switching element (12) of a higher (U ₁ ) to a lower (U ₂ ) voltage level, wherein the power supply (26) is a variable power supply with variable output voltage (U _A ), the lowering unit (30) depending on the operating state, the output voltage (U _A ) of the power supply (26) determines, and a start switch (38) is provided with a switch-on, the start switch (38) only in the presence of the higher voltage value (U ₁ ) of the operating voltage (U '_B; U _B ) releases.

Description

The The present invention relates to a safety switching device for safe Turning on and off an electrical consumer, in particular an electric drive, with an electromechanical switching element, having at least one adjustable working contact, with a Power supply for generating an operating voltage for the switching element, and with a lowering unit, which controls the operating voltage supplied to the switching element dependent on from an operating state of the switching element from a higher one lowers a lower voltage level.

One such safety switching device is known for its use.

Generic safety switching devices are mainly used in the industrial sector to electrically driven Machines, such as a press or a milling tool, one and especially safely turn off. They serve, for example, in conjunction with a mechanical actuatable emergency stop button to make the machine fast and safe in an emergency situation off. For this purpose, the power supply is the off Machine over guided the adjustable contact of the switching element. Frequently for safety reasons even working contacts of several redundant switching elements in Series arranged to each other, what for the present invention but not essential. As soon as the worker contacts open be, is the power supply interrupted the machine.

When Switching elements are usually relays, at high currents to be switched so-called Sagittarius used. Such switching elements have an input side Control circuit with a coil, using the supplied operating voltage a control current is generated. The control current in turn generates a magnetic field which, with sufficient strength, the or the working contacts into their active working position. In a so-called normally closed switching element the working contacts are open in the active state, in a so-called NO switching element closed. In the passive state of rest is the position of the working contacts in reverse, respectively.

One known problem with generic safety switching devices, the existence only a degree Heat with it no thermal damage results in the housing of the switchgear may be introduced. Much of this heat is created due to ohmic losses in the coils of the switching elements. to solution This problem is known, the operating voltage for the switching element after activating the working contacts to one as possible Lower low holding voltage. In contrast, to activate the work contacts a higher one Operating voltage required, because in this case the working contacts with the expenditure of a higher energy must be moved against a mechanical biasing force.

To the Lowering the operating voltage are in generic safety switching devices so far two different methods known. In the first case, then, if the working contacts of the switching element have gone into their working position are, a series resistor connected in the circuit of the switching element. The original applied operating voltage then shares the series resistor and the switching element, so that the switching element itself receives a lowered operating voltage. This method has however, the disadvantage that too the series resistor heat generated due to ohmic losses, so that overall only a comparatively low reduction of the thermal load can be achieved.

at The second known alternative is in the circuit that the Operating voltage leads to the switching element, a transistor arranged, the over a control circuit is clocked. By a clocking with variable Pulse width (pulse width modulation) can be the average operating voltage Lower at the switching element. Also with this alternative becomes However, with the transistor a component is needed which itself heat due produced its power loss. In addition, in this case the control of the transistor comparatively expensive.

State of the art

Out DE 29 48 954 C2 a general electromagnetic switching device is known which has an electromechanical switching element with a number of adjustable working contacts. A power supply for generating an operating voltage for the switching element is not disclosed here, however.

Out DE 40 24 496 A1 is a circuit arrangement for the operation of electromagnetic loads, in particular of solenoid valves, known. The circuit arrangement is connected to the electrical system of a motor vehicle and serves to generate after tightening the solenoid valve by means of the vehicle electrical system voltage a lower holding voltage. This is done by turning on a first transistor and a second transistor, the second transistor being arranged at the output of a voltage regulator which generates the lower holding voltage. A comparable arrangement is off DE 39 20 064 A1 known.

Out US 4,679,116 A a power control circuit for a relay is known, with the to tightening the relay required tightening tension can also be lowered to a lower holding value. This known circuit arrangement operates with a transistor as a variable resistor, at which a portion of the operating voltage not required for holding the relay drops. Said circuit arrangement is therefore comparable to the prior art generally described above.

Out DE 195 08 885 A1 a device for peak voltage generation in a transformer circuit is known. For example, the generated peak voltage serves as the pull-in voltage for a relay, while a lower (lowered) voltage is used as the hold voltage. The lowered holding voltage is, as generally described above, generated by means of a arranged in the longitudinal branch to the relay switching element from the provided mains voltage.

Out US 4,777,556 A is a further circuit arrangement for generating an excessive peak voltage known as a pull-in voltage for an electromagnetic device. In this case, too, a fixed power supply voltage is assumed, from which an excessive peak value is derived with the aid of the described circuit arrangement.

From the DE 199 30 994 A1 a safety circuit is known in which the operating voltage of a relay after a fixed period of about 100 ms from 12 V to 8 V is lowered in order to reduce the thermal load.

task

In front It is an object of the present invention to provide a specify another alternative, such as the thermal load at a safety relay of the type mentioned can be reduced. It should in particular a safety relay be given in a simple and efficient way a high pull-in voltage and a lower holding voltage for operation an electromechanical switching element are provided.

These Task is solved in the above-mentioned safety relay with the Features of claim 1.

in the Difference to the previously known measures is the lowering the operating voltage here, by the lowering unit directly the output voltage of the power supply. This implies the use of a variable output voltage power supply advance, which is unusual in previously known, generic safety switching devices. In contrast to the prior art, the "excess" operating voltage therefore already reduced at its source. In other words, that generates Power supply in the safety switching device according to the invention respectively only for needed the switching element Operating voltage. Deriving or "destroying" a power supply initially provided by the power supply but not needed Proportion of the operating voltage can thus be omitted.

The measure is easier compared to generic safety switching devices, because switchable series resistors or the measures for Clocks and pulse width modulation of the operating voltage omitted can. About that In addition, also accounts for this purpose so far th Building elements, each for generate heat as a result of power losses. Finally, at the solution according to the invention also the power supply losses reduced, since already from the power supply itself a lower operating voltage is generated.

All in all Therefore, the thermal load of the safety switching device according to the invention be significantly reduced. In addition, the arrangement according to the invention easier than the previously known switching devices.

there is guaranteed that this Safety relay Actually activate the normally open contacts of the switching element, when the start switch is pressed becomes. As a result, the behavior of the safety relay for a Operator more transparent and easier to understand. The danger of incorrect operations is reduced, which in particular with regard to on the safety aspect of the switching devices is an advantage.

The This task is therefore completely solved.

In An embodiment of the invention is the operating voltage supplied to the switching element via a additional Energy storage buffered.

When Energy storage is preferably a capacitor use, the additional, d. H. outside of the power supply is arranged. The measure has the advantage that this Switching element a very uniform and stable operating voltage, what the danger of interference and faulty switching operations reduced. This is especially with regard to the safety aspect the switching devices advantageous.

In a further embodiment, the switching element for activating the normally-open contact requires a maximum switching power and the power-supply unit has an electrical rated power that is lower than that maximum switching capacity is.

at This embodiment of the invention is the power supply in terms undersized to the maximum required switching capacity. The power supply is for itself not able to activate the working contacts provide required switching power. Because the maximum switching capacity However, only a short time when activating the work contacts needed, it can be provided by a prior charging of the additional energy storage. The additional Energy Saving is in contrast to the power supply in terms dimensioned to the maximum switching capacity.

in the Working operation of the safety relay, by contrast, is only a lower holding power for the working contacts required. This lower power can also of one with regard to the required switching capacity undersized power supply can be provided.

The measure has the advantage that due the lower rated power is a power supply with smaller transformer can be used, whereby the size is reduced. The safety switching device according to the invention this Design can therefore be realized very small building.

In Another embodiment of the invention is the operating state the achievement of a working position of the working contact.

These measure has the advantage that the Lowering the operating voltage as early as possible. This will be reduces the thermal loads of the safety relay early.

In Another embodiment of the invention is the output voltage of the power supply depending on controlled by an operating parameter of the switching element.

In This embodiment of the invention is not only the working position of the work contact, but there are also other operating parameters, such as an operating temperature, taken into account. This is it possible, to lower the operating voltage to an optimal value, whereby the thermal load of the safety relay again is reduced. At the same time due to the regulation is a faultless Guaranteed function of the safety relay.

In An embodiment of the aforementioned measure is the operating parameter an operating temperature of the switching element.

These measure is particularly advantageous because the ohmic resistance of coils increases with increasing temperature. Because with increasing resistance the current flow and hence the strength of the magnetic field decreases, without a temperature-dependent Control of the operating voltage takes into account a voltage reserve to ensure error-free operation of the safety relay to guarantee all working conditions. This voltage reserve is in terms of thermal load however disadvantageous, in this embodiment of the invention is avoided.

In Another embodiment of the invention is the operating parameter a holding current of the switching element.

at this embodiment of the invention is the respectively required Operating voltage determined by means of a current sensor, which in the Circuit for the switching element is arranged. The output voltage of the power supply is therefore determined by the Absenkeinheit each so that a constant Holding current flow can. The holding current for the switching element is impressed as it were. Even with this measure is an optimal regulation of the operating voltage for the reduction of thermal loads possible.

In In a further embodiment of the invention, the safety switching device has a timer a defined time constant and the lowering of the operating voltage takes place depending on the defined time constant.

These measure is circuit technology very easy and inexpensive to implement and can therefore for cost reduction instead of regulating the operating voltage be used. She can over it but also in addition to apply a scheme to the beginning of the actual Determine control process.

In a further embodiment of the aforementioned measure includes the timer the switching element.

This embodiment has the advantage that the timer implicitly, ie can be realized very inexpensively without the use of additional components. In this case, the timer is particularly preferably realized by charging an energy store, which provides the switching element with the required operating voltage, to a voltage value which is still above the higher voltage value in the sense of the present invention. The components involved are then dimensioned such that initial voltage decreases from its maximum value to the said higher voltage value in a period of time which is corresponds to the defined time constant.

It understands that the mentioned above and the features to be explained below not only in the specified combination, but also in other combinations or alone, without to leave the scope of the present invention.

embodiment

embodiments The invention are illustrated in the drawings and in the following description explained. Show it:

1 a schematic representation of a first embodiment of the invention;

2 a schematic representation of a second embodiment of the invention;

3 two voltage-time diagrams that make up the function of the safety relay according to 1 is apparent; and

4 two voltage-time diagrams of another embodiment.

In 1 is an inventive safety switching device in its entirety by the reference numeral 10 designated.

The safety relay 10 has an electromechanical switching element 12 in the form of a relay. The switching element 12 has in the present embodiment, three parallel to each other working contacts 14 , which are connected in series between each input terminal 18 and an output terminal 20 of the safety relay 10 are ordered to. To the input terminals 18 is a power supply in a conventional manner 22 for an electrical consumer 24 connected. The consumer 24 is in turn in a conventional manner to the output terminals 20 of the safety relay 10 connected. Exemplary here as an electrical consumer 24 an electric drive shown. The electric drive moves, for example, a milling head or a press.

Deviating from the illustration shown here, safety switching devices of the type shown often have two mutually redundant switching elements 12 , their working contacts 14 are each arranged serially to each other. This redundancy is a safe shutdown of the electrical load 24 even in case of failure of one of the switching elements 12 guaranteed. This embodiment is sufficiently well known in the prior art and has not been shown here for reasons of clarity.

With the reference number 26 is a power supply referred to, which is here according to a preferred embodiment of the invention, a switching power supply. The power supply 26 can be connected via two terminals 28 be connected in a conventional manner to a power supply. In a preferred embodiment this is the power supply 22 that is also the electrical consumer 24 supplied (not shown here).

The power supply 26 is a variable power supply with a variable output voltage.

With the reference number 30 is a schematically illustrated lowering unit referred to, in the manner explained below, the output voltage of the power supply 26 certainly. The lowering unit 30 However, it is not necessary as a separate component in the safety relay 10 contain. It can be spatially as well in the power supply 26 be integrated. This is preferably the case when the power supply 26 Already by itself can process the input signals described below for setting the variable output voltage. For power supplies 26 that can not process such signals directly includes the sinker 30 a signal conditioning and optionally a circuit logic that combines the various input signals described below.

In the embodiment shown here receives the lowering unit 30 the output signal of a temperature sensor 32 , the operating temperature θ of the switching element 12 determined. The lowering unit 30 determined in dependence on the obtained operating temperature θ, the output voltage U _{A of} the power supply 26 ,

With the reference number 34 is a capacitor called, which is parallel to the output of the power supply 26 is arranged. The capacitor 34 charges itself to the output voltage U _{A of} the power supply 26 and forms a capacitive energy storage. Parallel to the capacitor 34 is a voltage sensor 36 arranged on the capacitor 34 applied voltage value determined. The output signal of the voltage sensor 36 is a start switch 38 supplied serially in the voltage supply from the capacitor 34 to the switching element 12 is arranged. The start switch 38 has in the present embodiment, a not shown here in-circuit protection, the start switch 38 for an operator releases only when that of the voltage sensor 36 certain voltage value is sufficient to make the working contacts 14 to move to their working position. This required voltage value is preferably the higher voltage value in the sense of the present invention.

The in this embodiment of the switching element 12 applied voltage is denoted by U ' _B. It differs from the output voltage U _{A of} the power supply 26 and thus of the here at the condenser 34 applied voltage U _B in that they only on a successful operation of the start switch 38 jumps to the voltage value on the capacitor 34 is applied. The temporal relationships are described below on the basis of 3 explained in more detail.

According to a preferred embodiment of the invention, the start switch 38 about a timer 40 with the lowering unit 30 connected. The timer 40 has a defined time constant T. The lowering unit 30 thus receives a delayed by the time constant T signal when the start switch 38 has been successfully operated. The time constant T is chosen so that the switching element 12 within the resulting period of time the working contacts 14 moved to her job. The lowering unit 30 Therefore, in the presence of said signal, the output voltage U _{A of} the power supply 26 to a value sufficient to make the working contacts 14 in their working position. This voltage value is commonly used as a holding voltage of the switching element 12 and preferably corresponds to the lower voltage value in the sense of the present invention.

In a variant of this embodiment, the timer 40 be saved when the capacitor 34 is initially charged to a third voltage value, which is again higher than the already mentioned higher voltage value. The time until the capacitor 34 has then discharged to the said higher voltage value, corresponds to the time constant T. The operation of this variant is described below 4 explained in more detail.

In 2 is another embodiment of a safety switching device according to the invention in its entirety by the reference numeral 50 designated. The same reference numerals designate the same elements as in FIG 1 ,

In contrast to the embodiment according to 1 becomes the output voltage U _{A of} the power supply 20 in the safety relay 50 not in dependence on an operating temperature θ of the switching element 12 , but regulated as a function of the required holding current I _H. The holding current I _H denotes the current that is required to the working contacts 14 of the switching element 12 in their active employment.

For determining the switching element 12 supplied current I _H is in the present embodiment, serial to the start switch 38 a resistance 52 arranged, whose respective voltage drop in a conventional manner by means of a voltage sensor 54 is measured. The output signal of the voltage sensor 54 is the lowering unit 30 supplied, in response to the output voltage U _{A of} the power supply 26 certainly. Otherwise, the operation of the safety relay corresponds 50 that of the safety relay 10 ,

Representative also for further embodiments is in 3 Using two voltage-time diagrams, the operation of the safety relay 10 explained, in these diagrams, the timer 40 is taken into account.

The upper timing diagram shows the variation of the voltage U _B across the capacitor 34 , At the same time, this is the course of the switching element 12 applied operating voltage U ' _B shown.

After commissioning of the safety relay 10 becomes the capacitor 34 over the power supply 26 to a higher voltage value, which is here designated U ₁ , charged. The voltage value U ₁ is reached at time t ₀ . From this point has the capacitor 34 the required voltage to the switching element 12 to activate his working contacts 14 to deliver required power. At time t ₁ , the start switch 38 operated by an operator. An operation of the start switch 38 at an earlier time than t ₀ would have no effect, since the switch-on fuse the start switch due to the not yet sufficiently charged capacitor 34 has not yet released.

By successfully pressing the start switch 38 becomes the capacitor 34 with the switching element 12 connected. The operating voltage U ' _B therefore jumps to the value of the capacitor 34 applied voltage U _B.

After the expiration of the timer 40 predetermined period T controls the lowering unit 30 the power supply 26 such that the voltages U _B and U ' _B drop to a lower voltage value U ₂ . The time T is chosen so that the normally open contacts 14 of the switching element 12 already moved to their active employment position at that time.

The lower voltage value U ₂ corresponds to the required holding voltage of the switching element 12 , According to a preferred embodiment of the invention, the voltage value U ₂ further corresponds to the voltage at which the power supply 26 delivers its nominal power to a matched resistor. This value, referred to here as rated voltage, is in the two time diagrams of FIG 3 by a dotted line 60 shown. As can be seen, is the nominal voltage of the power supply 26 below the voltage value U ₁ , to which the capacitor 34 before pressing the start switch 38 must be charged. The power supply 26 is therefore undersized with regard to the maximum required switching capacity.

In the already mentioned variant of in 1 The embodiment shown is the function of the timer 40 implicitly realized by the fact that the capacitor 34 is initially charged to a voltage value U ₃ , which is again higher than the said higher voltage value U ₁ . This is in 4 shown. After pressing the start switch 38 at time t ₁ , the capacitor can 34 over the switching element 12 discharged. The voltage U _B on the capacitor 34 decreases accordingly. The capacitor 34 and the discharge resistors are dimensioned so that the voltage U _B or U ' _B only after the expiration of the time T to activate the normally open contacts 14 required voltage U ₁ falls below. The lowering unit 30 can the power adapter 26 therefore already from the moment to drive, to which the start switch 38 is pressed.

Claims (9)

Safety switching device for safe switching on and off of an electrical consumer ( 24 ), in particular an electric drive, with an electromechanical switching element ( 12 ), which has at least one adjustable working contact ( 14 ), with a power supply ( 26 ) for generating an operating voltage (U '_B; U _B ) for the switching element ( 12 ), and with a lowering unit ( 30 ), which the switching element ( 12 ) supplied operating voltage (U '_B; U _B ) in dependence on an operating state of the switching element ( 12 ) from a higher (U ₁ ) to a lower (U ₂ ) voltage level, whereby the power supply ( 26 ) is a variable power supply with variable output voltage (U _A ), the lowering unit ( 30 ) depending on the operating state, the output voltage (U _A ) of the power supply ( 26 ), and a start switch ( 38 ) is provided with a switch-on, which the start switch ( 38 ) only in the presence of the higher voltage value (U ₁ ) of the operating voltage (U ' _B , U _B ) releases. Safety switching device according to claim 1, characterized in that the switching element ( 12 ) supplied operating voltage (U ' _B , U _B ) via an additional energy storage ( 34 ) is buffered. Safety switching device according to claim 2, characterized in that the switching element ( 12 ) to activate the working contact ( 14 ) requires a maximum switching power, and that the power supply ( 26 ) has an electrical rating that is less than the maximum switching power. Safety switching device according to one of Claims 1 to 3, characterized in that the said operating state indicates the reaching of a working position of the working contact ( 14 ). Safety switching device according to one of claims 1 to 4, characterized in that the output voltage (U _A ) of the power supply ( 26 ) in dependence on an operating parameter (θ; I _H ) of the switching element ( 12 ) is regulated. Safety switching device according to Claim 5, characterized in that the operating parameter has an operating temperature (θ) of the switching element ( 12 ). Safety switching device according to Claim 5 or 6, characterized in that the operating parameter (I _H ) is a holding current of the switching element ( 12 ). Safety switching device according to one of Claims 1 to 7, characterized in that it has a timer ( 40 ) with a defined time constant (T) and that the lowering of the operating voltage (U ' _B ) takes place as a function of the defined time constant (T). Safety switching device according to Claim 8, characterized in that the timer ( 40 ) the switching element ( 12 ) includes.